Processes that are conventionally known include a process to form a wiring in a wiring groove, a hole, or a resist opening that is very small in size and is provided on a surface of a semiconductor wafer or the like and a process to have a bump (a projection-shaped electrode) that is electrically connected to an electrode in a package or the like formed on a surface of a semiconductor wafer or the like. As methods for forming such a wiring or a bump, for example, electroplating methods, vapor deposition methods, printing methods, and ball bump methods are known. In recent years, as the number of inputs/outputs (I/O) of semiconductor chips increases and as the pitch becomes smaller, electroplating methods have become more popular, because electroplating methods allow miniaturization and the performance thereof is relatively stable.
A plating apparatus used in an electroplating method includes: a substrate holder that holds a substrate such as a semiconductor wafer or the like; an anode holder that holds an anode; and a plating bath that contains a plating solution including a large number of types of additives. When the plating apparatus performs a plating process on the surface of the substrate (e.g., the semiconductor wafer), the substrate holder and the anode holder are arranged so as to face each other in the plating bath. In this state, when an electric current is arranged to flow between the substrate and the anode, a plating film is formed on the surface of the substrate. The additives have, among others, an effect of accelerating or decelerating the speed at which the plating film is formed, as well as an effect of improving the quality of the plating film.
Conventionally, as an anode held by an anode holder, a soluble anode that can be dissolved in a plating solution or an insoluble anode that is not dissolved in a plating solution has been used. When a plating process is performed by using an insoluble anode, oxygen is generated by a reaction between the anode and the plating solution. The additives in the plating solution are decomposed by reacting with the oxygen. When the additives are decomposed, a problem arises where the additives lose the abovementioned effects and it becomes impossible to form a desired film on the surface of the substrate (see Patent Literature 1, for example). Further, when phosphorus-containing copper is used as a soluble anode, for example, it is known that the quality of the additives, especially accelerants, changes due to a reaction with monovalent copper generated from the anode during non-electrolysis time periods.
Further, when phosphorus-containing copper is used as a soluble anode, for example, a so-called black film, which is a phosphate coating film, is formed on the surface of the anode as the anode is electrolyzed during the plating process (see Non-Patent Literature 1, for example). There is a possibility that such a black film may come off the surface of the anode during the plating process. When the black film that came off the surface moves through the plating solution and adheres to the surface of the substrate, no plating film is formed in such a part of the surface of the substrate to which the black film adhered. Consequently, a problem arises where the plated surface has a defect, and the yield and the reliability of the final product is degraded. To cope with this situation, an anode holder is known with which a diaphragm is provided for the purpose of inhibiting additives from being decomposed and inhibiting black films from adhering to the surface of a substrate (see Patent Literature 2, for example).
FIG. 16 is a partial cross-sectional view of a conventional anode holder including a diaphragm. As illustrated in FIG. 16, an anode holder 110 includes: an anode 105; an anode holder base 111 that has a space for housing the anode 105 therein; an anode mask 113 attached to the front face of the anode holder base 111; a diaphragm 150 attached to the front face of the anode mask 113; a contact member 102 that is electrically conductive and is in contact with the rear face of the anode 105; and a power supply member 103 that is electrically conductive and extends from the rear face of the contact member 102 so as to be connected to an external electrode (not illustrated).
The anode holder base 111 has a hole 112 which communicates with the space housing the anode 105 therein. When the anode holder 110 is soaked in a plating solution, the plating solution flows into the space housing the anode 105 therein by going through the hole 112, so that the anode 105 is soaked in the plating solution. The contact member 102 is able to supply an electric current from the external electrode to the anode 105 via the power supply member 103. With this arrangement, when the anode holder 110 is soaked in the plating solution, an electric current flows between the anode 105 and the substrate via the plating solution.
The diaphragm 150 is an ion exchange membrane, for example, and is provided so as to separate the front face of the space housing the anode 105 therein from the external space of the anode holder 110. Cations that are generated in the vicinity of the anode 105 are able to reach the surface of the substrate by passing through the diaphragm 150. In addition, the diaphragm 150 is able to prevent any black film formed on the surface of the anode 105 from going therethrough and is thus able to inhibit the black film from spreading in the plating bath. Further, the diaphragm 150 inhibits the additives contained in the plating solution from reaching the anode 105 and thus inhibits the additives from being decomposed.